A highly variable portion of the mitochondrial DNA control region was sequenced in 63 free-living and captive gorillas including representatives of the three recognized subspecies. This region has proven useful for evaluation of relative levels of genetic variability in populations, for clarification of the subspecies identity of a wild population, and for examination of the phylogenetic relationships of the three subspecies. The eastern lowland (Gorilla gorilla graueri) and mountain gorilla (Gorilla gorilla beringei) sequences are distinct but closely related, with low variability within each subspecies. Two currently isolated populations of mountain gorillas, one in the Virungas Volcanoes region and the other in the Bwindi Forest, are indistinguishable using this mitochondrial DNA region for comparison. The subspecies identity of the Bwindi Forest group has previously been debated. Mitochondrial D-loop DNA variability within the western lowland gorillas (Gorilla gorilla gorilla) is very high. The genetic distance between the most divergent gorilla sequences is approximately as great as the distance between sequences of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus).